Japanese unexamined patent application publication No. JP-A-2007-079121 describes a related art image forming apparatus such as a laser printer. The related art image forming apparatus has a photosensitive body on which an electrostatic latent image is formed by being exposed to light in accordance with an image to be formed, and a development cartridge for supplying a developer (toner) to the photosensitive body. Although the photosensitive body is an expendable item, the service life thereof is not coincident with the period of use in which toner is consumed in the development cartridge. Therefore, the photosensitive body is constructed so as to be replaced in the form of another cartridge (photosensitive cartridge) separate from the development cartridge.
Consumption of the photosensitive cartridge and the development cartridge may be checked by counting the number of times of image formation. Therefore, it is necessary to securely detect mounted states of the photosensitive cartridge and the development cartridge.
Therefore, the above described related art image forming apparatus has a technology for detecting toner cartridge (development cartridge) and a drum cartridge (photosensitive cartridge). In the related art image forming apparatus, using optical sensors to detect toner being empty, it is determined whether or not toner exists, whether a toner cartridge exists and whether a drum cartridge exists. In detail, in the toner cartridge, optical sensors are placed with the toner accommodating chamber disposed therebetween, and a window is provided at the position corresponding to a light path of the optical sensors on the wall of the toner accommodating chamber. And, the window is periodically cleaned by a wiper to ensure passing of light, and light is temporarily interrupted by passing of the wiper. In addition, a through hole is formed at the front side of the window on the wall of the drum cartridge opposed to the window, and at the same time, an interrupting member (shutter), which is opened in accordance with mounting of the toner cartridge, is provided at the through hole portion.
With such a configuration, the determinations described above are carried out by detection states of light by the optical sensors. That is, the quantity of toner is detected by the ratio of the period during which light is detected. If no light is detected, it is determined that the toner cartridge is not mounted, and if light is continuously detected, it is determined that the drum cartridge is not mounted.